A composite image forming apparatus (called an MFP) having plural functions, such as a copy function, a scan function and a print function, can copy an image of a document. Besides, this MFP can print image data transmitted from a network-connected external equipment, for example, a personal computer.
The power consumption of a building, for example, an office where such MFPs and personal computers are installed is very large. When the power consumption exceeds a rated value, a breaker of the office operates, and the supply of electric power to the MFPs and the personal computers is stopped.